In motor vehicles, during travel resonances occur during which the passenger compartment of the motor vehicle is excited by an open window or open sunroof. The passenger compartment of the motor vehicle acts here as a Helmholtz resonator whose actual frequency depends essentially on the volume of the passenger compartment of the motor vehicle. When a resonance occurs, coherent vortex structures are shed at the front edge of the window opening or sunroof opening, and they strike the rear edge and lead there to pressure waves which excite the passenger compartment of the vehicle and lead in turn to the occurrence of new vortex shedding at the front edge of the opening.
Whether or not resonance occurs is dependent on the relative speed of the vortex structures, which speed is in turn influenced by the instantaneous speed of the motor vehicle. What is referred to as booming noise occurs only in limited speed ranges, but is unpleasant for the occupants of the motor vehicle since such noise is associated with sound pressures of up to approximately 130 dB at frequencies of around 20 Hz.
A reduction in this sound pressure and therefore a reduction in the booming noise can basically be brought about by preventing the vortex structures from striking the rear edge of the window opening or sunroof opening of the motor vehicle.
For this purpose, it has already been proposed to bring about a reduction in booming noise by moving the sunroof of a motor vehicle into a comfort position in which the angle of aperture of the sunroof is restricted.
Furthermore, for this purpose it has already been proposed to position a wind deflector in front of the sunroof in order to move the point where the shedding formed at the front edge strikes regions behind the sunroof opening.
Furthermore, it is already known to provide such a wind deflector with vortex generators which disrupt the regulatory of the specified shedding. Such vortex generators are, for example, notches, slits, grooves, knobs or drilled holes in the wind deflector or tongues which are provided at a suitable location and which oscillate in the air stream.
In addition, it has already been proposed to reduce sunroof booming by mounting a movable lip on the front edge of the sunroof, wherein this movable lip is excited by actuators, for example with a noise signal, and in this way said lip disrupts the periodic excitation. The use of such a movable lip is described, for example, in section 7.3.6 on pages 443-445 of the book Aerodynamic des Automobils [Motor vehicle aerodynamics], Vieweg+Täubner, 5th edition, ISBN 9783-3-528-03959-2, by Wolf-Heinrich Hucho.
DE 100 56 754 A1 discloses a wind deflector for a sunroof opening of a motor vehicle whose wind deflector profile has, on an end side thereof, a series of air inlet openings which are arranged distributed over the width of said wind deflector profile, and has on an adjacent profile side a row with air outlet openings. The wind deflector profile is embodied as a hollow profile, wherein the upper boundary wall of the wind deflector profile is penetrated by the air outlet openings.
DE 199 58 748 B4 discloses a device for influencing the air stream in the region of the roof opening of a vehicle roof. This known device has a wind deflector which is arranged in a vertically adjustable fashion in the region of the front edge of the roof opening between a position of rest, in which the upper side of the wind deflector does not project beyond the fixed roof surface, and a first extended position. In this first extended position, the upper side of the wind deflector projects beyond the fixed roof surface. An air stream which flows over the vehicle roof is directed exclusively over the upper side of the wind deflector. Furthermore, the specified wind deflector can be moved into a second extended position in which an air stream which flows over the vehicle roof is directed through at least partially under the wind deflector, in order to reduce booming noise.